## Standards derived from the same national standard

Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.

Mentally add or subtract 10 to or from a given two-digit number. Explain the reasoning used.

Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.

Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.

Given a two-digit number, mentally find 10 more or 10 less than the number without having to count; explain the reasoning used.